CN101615677A - Electrocatalyst for fuel cell membrane electrode, preparation method thereof and fuel cell membrane electrode - Google Patents

Abstract

The invention relates to the field of fuel cells, and discloses an electrocatalyst for a fuel cell membrane electrode, a preparation method thereof, and a fuel cell membrane electrode. An electrocatalyst for a membrane electrode of a fuel cell, characterized in that: the electrocatalyst is prepared by loading a precious metal on a composite carrier, and the composite carrier is a carbon carrier deposited by a water-retaining substance; in the electrocatalyst, the water-retaining substance The content of the precious metal is 0.3-10wt%; the content of the precious metal is 10-60wt%. Using the electrocatalyst of the present invention as the anode catalyst, the electrode is prepared in a conventional manner; a membrane electrode with excellent moisturizing performance can be obtained; there is no need to build a water-retaining layer, and it is not necessary to add water-retaining substances to the proton exchange membrane, avoiding water retention. It is a simple and efficient way to prepare a humidification-free membrane electrode due to the increase of the internal resistance of the battery caused by the addition of water-retaining substances in the layer and the proton exchange membrane.

Description

Electrocatalyst for fuel cell membrane electrode, preparation method thereof and fuel cell membrane electrode

technical field

The invention relates to a fuel cell. An electrocatalyst with self-humidification function in the fuel cell is prepared, and a membrane electrode with good self-humidification performance is prepared by using the electrocatalyst.

Background technique

In proton exchange membrane fuel cells (PEMFCs), water management has a decisive impact on cell performance. When PEMFC is running, it is usually necessary to humidify the reaction gas externally to ensure that there is enough water in the proton exchange membrane and electrodes to obtain high proton conductivity and electrochemical performance. Gas humidification is generally completed by complex auxiliary humidification equipment. The humidification system increases the complexity of the PEMFC system and increases the cost of the PEMFC system. At the same time, external humidification needs to consume a lot of energy, which reduces the total output power of the fuel cell system; in fact, a large amount of water will be generated on the anode of the proton exchange membrane fuel cell during operation, so some researchers hope to use The generated water is used to realize self-humidification or non-humidification membrane electrodes and corresponding fuel cell systems; in fact, the development of fuel cell membrane electrodes with non-humidification/self-humidification functions has become a research topic in the field of fuel cells. One of the hottest topics.

The current research on non-humidification/self-humidification fuel cell membrane electrodes mainly focuses on the following aspects: 1) developing a composite proton exchange membrane with moisturizing function by adding water-retaining substances; 2) adding precious metals to the proton exchange membrane The proton exchange membrane with moisturizing function is prepared by catalyst method. The principle is to use the hydrogen and oxygen permeated into the membrane to generate water in the membrane to realize the moisture retention of the membrane; 3) between the catalytic layer and the proton exchange membrane Add a moisturizing layer to achieve non-humidification/self-humidification; 4) add water-retaining substances to the catalytic layer to achieve non-humidification/self-humidification of the membrane electrode; unfortunately: so far, these methods cannot obtain Ideal non-humidification/self-humidification effect. In addition, some researchers hope to achieve self-humidification or non-humidification through the design and modification of the flow field, but the effect is far from meeting the needs of high-performance fuel cells for humidification-free membrane electrodes.

Watanabe et al. (Watanabe M., Uchida H., Seki Y., et al. J. Electrochem. Soc., 1996, 143: 3847-3852.) recast highly dispersed Pt particles and metal oxides in Nafion solution In film formation, the role of Pt particles is to catalyze the reaction of _H2 and _O2 permeating into the membrane to generate water, and the role of oxides is to keep the generated water in the membrane. Battery tests show that this composite membrane has high performance and good stability under normal pressure and low humidity conditions (H ₂ humidification temperature is 20 ° C, O ₂ is not humidified), and when the current density is 0.9Acm ^-2 , the power density of the battery can reach 0.63Wcm ^-2 . Since then Watanabe and his collaborators (Watanabe M., Uchida H., Emori MJPhys.Chem.B, 1998, 102: 3129-3137, Watanabe M., Uchida H., Emori MJ Electrochem.Soc., 1998, 145: 1137- 1141, Uchida H., Mizuno Y., Watanabe M., et al. J. Electrochem. Soc., 2003, 150: A57-A62, Hagihara H., Uchida H., Watanabe M. Electrochim. Acta, 2006, 51 : 3979-3985) conducted in-depth research and optimization on this method. However, this method has troubles in preparation, and the effect of avoiding humidification cannot meet the requirement of long-term stability.

Chinese patent ZL02103832.5 discloses a method for preparing a self-moisture composite membrane for a proton exchange membrane fuel cell, that is, a proton exchange membrane and a coating with a moisture retention function are combined to form a composite membrane. The preparation method of the composite film of this patent is: uniformly mix 0.1-10 μm inorganic substances or their oxides, organic substances with the same composition as the organic film, and organic solvents to make a slurry, then coat the surface of the organic film, and dry , Curing is obtained from the moisturizing composite film. The preparation process of this method is complicated, and the particle size of the inorganic substance or its oxide in the moisturizing coating is too large, which will affect the transfer of protons, thereby reducing the performance of the membrane electrode. Therefore, this method is not suitable for large-scale application to proton exchange membranes. The fuel cell.

Chinese patent ZL02122635.0 discloses "a method for preparing a self-humidifying composite proton exchange membrane for fuel cells". This patent application heats and dissolves perfluorosulfonic acid membranes in a solvent of low-boiling organic alcohol and water to produce perfluorosulfonic acid membranes. Acid resin solution, and then add Pt-containing supported catalyst and high-boiling point organic solvent to the perfluorosulfonic acid resin solution, add the solution dropwise on the surface of the organic porous membrane, heat and store in vacuum to obtain a self-humidifying composite membrane. This method adds a catalyst to the membrane, which is likely to cause a short circuit between the cathode and the anode and reduce the performance of the battery, so it is not suitable for practical applications.

Chinese patent ZL03140527.4 discloses a "self-humidifying solid electrolyte composite membrane and its preparation process". The preparation process of the solid electrolyte membrane is to dissolve the sulfonated resin in anhydrous A solution is obtained in an alcoholic solvent, and the crystal hydrate is broken into 5-100nm particles at 100-600MPa, and then dissolved in an anhydrous alcoholic solvent at 0.5-8MPa and 110-300°C to obtain a B solution. The solution is mixed uniformly at 0.5-8MPa and 200-650°C, then cooled to 150-580°C to form a film by casting method, dried at room temperature and then placed in an inert environment at 80-550°C for heat treatment to obtain a finished film. The preparation process of this method is complicated, and the conductivity of the prepared solid electrolyte composite membrane is low.

Chinese patent ZL200510018545.6 discloses a "preparation method of non-humidification proton exchange membrane for fuel cells", first dissolving the aromatic heterocyclic polymer containing sulfonic acid side groups in an organic solvent to form a uniform polymer solution, and then The gel formed by adding the oxide precursor and the inorganic acid is ultrasonically dispersed to obtain a uniform mixed liquid, and finally the membrane is doped twice to obtain a non-humidification proton exchange membrane. This method requires secondary doping, and the preparation is complicated, and the applicant did not give the battery performance of the prepared humidity-free proton exchange membrane.

Chinese patent ZL200510018740.9 discloses a "preparation method of proton exchange membrane fuel cell chip with water retention function". Particle layer, and finally, two electrodes with water retention function and proton exchange membrane are hot pressed to obtain a fuel cell chip. The water-retaining layer prepared by this method will increase the proton transfer resistance of the membrane electrode.

Chinese patent ZL200510067575.1 discloses "a self-humidifying membrane electrode and its preparation method". In this method, a self-humidifying membrane electrode is prepared by adding a hydrophilic substance to the anode catalytic layer and a hydrophobic substance to the cathode catalytic layer. . The hydrophilic and hydrophobic substances used in this patent will increase the charge transfer resistance of the catalytic layer.

Chinese patent ZL200610015662.1 discloses "a self-humidifying proton exchange membrane fuel cell membrane electrode". The wet layer is used to realize the self-humidification of the membrane electrode. The constant humidity layer of the self-humidifying membrane electrode prepared by this method will affect the diffusion of the reaction gas.

Chinese patent ZL200610134078.8 discloses "a carbon nanotube-reinforced self-humidifying composite proton exchange membrane and its preparation". There are two options for this method. The first option is to add Pt/CNTs to the perfluorosulfonic acid resin solution , ultrasonically disperse evenly, cast into a film, and then spray a certain thickness of perfluorosulfonic acid resin on both sides of the film, keep it in a vacuum oven at 120-200°C for 0.5-20h, and cool to obtain a three-layer composite film; scheme two It is to add CNTs to perfluorosulfonic acid resin respectively, cast into a CNTs film, and then spray the perfluorosulfonic acid resin solution containing Pt/ _SiO2 on both sides of the film, dry and cool to obtain a three-layer composite film. The conductivity of the composite membrane prepared by this method is reduced due to delamination, and the addition of SiO ₂ will reduce the proton conductivity of the membrane.

So far, none of these methods can obtain ideal non-humidification/self-humidification effects.

Contents of the invention

The object of the present invention is to provide an electrocatalyst used for fuel cell membrane electrodes.

The object of the present invention is also to provide a method for preparing the above-mentioned electrocatalyst for fuel cell membrane electrodes.

The purpose of the present invention is also to provide a self-humidification/humidification-free fuel cell membrane electrode, by using the above-mentioned electrocatalyst to realize the self-humidification/humidification-free of the membrane electrode, so that the fuel cell has excellent humidification-free/humidification-free Self-humidifying properties.

An electrocatalyst for a membrane electrode of a fuel cell, characterized in that: the electrocatalyst is prepared by loading a precious metal on a composite carrier, and the composite carrier is a carbon carrier deposited by a water-retaining substance; in the electrocatalyst, the water-retaining substance The content of the metal is 0.3-10wt%; the content of the noble metal is 10-60wt%.

Further, the water-retaining substance is one or more of silicon dioxide, titanium dioxide, ceria, zirconium dioxide, tungsten trioxide and molybdenum trioxide.

Further, the noble metal is platinum.

A method for preparing an electrocatalyst for a fuel cell membrane electrode, characterized in that it comprises the following steps:

(1) Dissolve the organic precursor of the water-retaining substance in a volatile organic solvent, then add the pretreated carbon carrier, stir at room temperature to mix the organic precursor of the water-retaining substance evenly on the carbon carrier, and then place it In a vacuum drying oven at 40-70°C, remove the volatile organic solvent by vacuuming, take it out and heat-treat it at 200-600°C for 1-5h under an inert gas atmosphere, and obtain a carbon carrier deposited by a water-retaining substance after cooling, that is, a composite carrier;

(2) Using the composite carrier prepared in step (1) as a carrier to prepare an electrocatalyst loaded with precious metals on the composite carrier; in the electrocatalyst, the content of the water-retaining substance is 0.3-10wt%, and the content of the noble metal is 10-60wt%.

In step (2), methods such as organosol method, impregnation method, and solid phase reduction method can be used to prepare the electrocatalyst loaded with noble metal on the composite carrier.

The carbon carrier is XC-72R carbon black, activated carbon and other carbon materials with good conductivity. The volatile organic solvents include low-boiling organic substances such as absolute ethanol and acetone. The water-retaining substance is hydrophilic oxides such as silicon dioxide, titanium dioxide, ceria, zirconium dioxide, tungsten trioxide, molybdenum trioxide, or a composite of two or more of these oxides. The organic precursors of the water-retaining substances are organic substances such as silicon and titanium, such as ethyl orthosilicate, ethyl titanate and the like.

A fuel cell membrane electrode includes a proton exchange membrane, an anode and a cathode, the proton exchange membrane is sandwiched between the two electrodes, and the feature is that the above-mentioned electrocatalyst is used as the anode catalyst.

Further, the cathode catalyst of the membrane electrode also adopts the above-mentioned electrocatalyst.

Preparation of humidification-free membrane electrode: the above-mentioned electrocatalyst is used as the anode catalyst, and the commercial catalyst or the above-mentioned electrocatalyst is used as the cathode catalyst, and the membrane electrode with good self-humidification/self-humidity performance can be prepared by direct coating technology and conventional electrode preparation procedures .

Compared with the existing fuel cell humidification-free technology, the present invention has the following advantages:

(1) A fuel cell catalyst with self-humidification/self-humidification function with excellent performance can be obtained by treating the catalyst carrier with a specific substance. This catalyst is directly used to prepare electrodes in a conventional manner; excellent moisture retention performance can be obtained Membrane electrode; there is no need to build a water-retaining layer, and there is no need to add water-retaining substances in the proton exchange membrane, which avoids the increase of internal resistance of the battery caused by the water-retaining layer and the addition of water-retaining substances in the proton exchange membrane. Therefore, this approach It is a simple and efficient way to prepare humidification-free membrane electrodes; it is extremely beneficial for large-scale preparation of humidification-free membrane electrodes for proton exchange membrane fuel cells;

(2) The catalyst with humidification-free function prepared by the method of the present invention does not require special equipment, the preparation process is simple, and large-scale preparation of the catalyst can be realized;

(3) The membrane electrode made of the catalyst prepared by the present invention, under the condition that hydrogen is used as fuel, air is used as oxidant, and the two gases are not humidified at all, the performance of non-humidification is better than that of previous reports. result.

Description of drawings

Fig. 1 is the performance curve that adopts the Pt/SiO2/C catalyst that contains 0.3wt% silicon dioxide to make as the membrane electrode that anode catalyst makes in hydrogen-air fuel cell;

Fig. 2 is the performance curve of the membrane electrode that adopts the Pt/SiO2/C catalyst that contains 3wt% silicon dioxide to make as anode catalyst in hydrogen-air fuel cell;

Fig. 3 is the performance curve of the membrane electrode that adopts the Pt/SiO2/C catalyst that contains 6wt% silicon dioxide to make as anode catalyst in hydrogen-air fuel cell;

Fig. 4 is the performance curve of the membrane electrode that adopts the Pt/SiO2/C catalyst that contains 9wt% silicon dioxide to make as anode catalyst in hydrogen-air fuel cell;

Fig. 5 is the performance contrast curve of the membrane electrode that adopts the Pt/SiO2/C catalyst that contains 3wt% silicon dioxide to make and the membrane electrode that adopts commodity Pt/C catalyst to make as anode catalyst in hydrogen-air fuel cell .

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

The specific implementation method of the present invention is as follows: first, the organic precursor of the water-retaining substance and the carbon carrier are used to prepare a composite carrier, and then the precious metal is uploaded to the composite carrier by an organic sol method to prepare an electrocatalyst, and the electrocatalyst of the present invention is used as the anode catalyst , the commercial catalyst or the electrocatalyst of the present invention is a cathode catalyst, and a film-forming electrode is prepared, and then assembled into a battery.

Example 1

(1) Preparation of composite carrier: Take 0.0155g of tetraethyl orthosilicate and add it to 3ml of ethanol, then add 1 gram of XC-72R carbon black that has been oxidized and heat-treated, and stir at room temperature for 15 minutes to make orthosilicate and carbon black uniform Disperse, then in a vacuum drying oven at 40°C, vacuumize to remove residual ethanol, then heat treat at 300°C for 3h under an inert atmosphere, and cool; that is, a carbon composite carrier material containing silicon dioxide is obtained; it can be expressed as SiO2 /XC-72R or SiO2/C;

(2) Preparation of electrocatalyst: take the composite carrier prepared in step (1) as the carrier, and adopt the organic sol method described in patent ZL200510102382. A mixture of acetone and ethylene glycol is used as a solvent, ethylene glycol is used as a reducing agent, chloroplatinic acid is used as a precursor of platinum, and sodium citrate is used as a complexing agent. React in an autoclave at 120 ° C for 8 hours, and then pass through a medium and degelling, washing, and drying to obtain an electrocatalyst;

In the prepared electrocatalyst, the platinum content is 25wt%, and the SiO2 content is 0.3wt%.

(3) Preparation of humidification-free membrane electrode: using the above catalysts as anode and cathode catalysts, a membrane electrode was prepared by using a direct film coating technology under light (ZL200610035275.4), and the platinum loading of the anode and cathode were 0.1mg /cm ² and 0.2mg/cm ² ; the specific steps are as follows: (A) fix the proton exchange membrane through hydrogen peroxide oxidation and sulfuric acid solution acid treatment on the frame mold; (B) fix the mold with the proton exchange membrane Placed under an infrared lamp, a certain amount of catalyst slurry is evenly sprayed on both sides of the proton exchange membrane with a spray gun to form a cathode and an anode; (C) in the catalyst slurry, the ratio of catalyst to dry Nafion is 2.5:1; Isopropanol was used as solvent.

(4) Test of the membrane electrode: the performance of the membrane electrode prepared was tested in the Arbin FCTS fuel cell system. The membrane electrode is activated under the condition that the humidification temperature of hydrogen and air and the temperature of the battery are both 60°C, and then the temperature of the dew point humidifier of air and hydrogen is lowered to room temperature, that is, the performance of the electrode under the condition of no humidification For testing, the battery temperature is 50°C, and the current density at a voltage of 0.6V is recorded at different times.

The obtained results are shown in Figure 1. Within 5 hours, the current density dropped from 900mA/cm ² to 450mA/cm ² , and then remained basically unchanged for 20 hours, showing a certain effect of avoiding humidification.

Example 2

Except that the amount of tetraethyl orthosilicate added is 0.155g, and the SiO2 content is 3% in the catalyst prepared at last, other steps are completely identical with embodiment 1.

The results show that: the membrane electrode made of Pt/SiO ₂ /C catalyst with SiO ₂ content of 3% shows a very good humidification-free effect, and the current density is only reduced by 200A/cm ² (from 900mA/ cm ² decreased to 700mA/cm ² ), and then basically remained unchanged within 20 hours (see Figure 2).

comparative example

Except adopting the commercial Pt/C catalyst (Johnson Matthey, Hisspec 4100,40wt%Pt) that does not contain silicon dioxide to replace the composite catalyst in Example 1, other membrane electrode preparation steps and testing steps are the same as the steps in Example 1 ( 3) is the same as (4);

The results show that the membrane electrode made of the catalyst without silica has no ability to avoid humidification, and the current density drops from 900mA/cm ² to below 100mA/cm ² within 3 hours (see Figure 5).

Example 3

In addition to increasing the amount of ethyl orthosilicate, and using acetone to replace absolute ethanol as the dispersion medium of ethyl orthosilicate, so that the _SiO2 content in the catalyst Pt/ _SiO2 /C that is finally prepared is 6%. , other with embodiment 1.

The results are shown in Figure 3 and Table 1. Its anti-humidification effect is lower than that of the membrane electrode prepared by the catalyst containing 3% silicon dioxide.

Example 4

Except that the amount of tetraethyl orthosilicate used is 0.465g, the _SiO2 content in the catalyst Pt/ _SiO2 /C that is finally prepared is 9%, the temperature and time of roasting in an inert atmosphere after impregnating tetraethyl orthosilicate Be respectively 600 ℃ and 1 hour, other are the same as embodiment 1.

The results are shown in Fig. 4 and Table 1, and the humidification-free effect is lower than that of the membrane electrode prepared by the catalyst containing 3% silicon dioxide, and also lower than that of the membrane electrode prepared by the catalyst containing 6% silicon dioxide.

Example 5

(1) Preparation of composite carrier: Take 0.5g ethyl orthosilicate and add it to 3ml ethanol, then add 1 gram of XC-72R carbon black that has been oxidized and heat-treated, and stir at room temperature for 15 minutes to make orthosilicate and carbon black uniform Disperse, then in a vacuum oven at 70°C, evacuate to remove residual ethanol, then heat treat at 200°C for 5h under an inert atmosphere, and cool down; that is, a carbon composite carrier material containing silicon dioxide is obtained; it can be expressed as SiO2 /XC-72R or SiO2/C;

(2) Preparation of electrocatalyst: with the composite carrier prepared in step (1) as the carrier, the organosol method described in the patent (ZL 200510102382.X) was used to prepare the noble metal electrocatalyst supported by the composite carrier; the specific method The method is: using a mixture of acetone and ethylene glycol as a solvent, ethylene glycol as a reducing agent, chloroplatinic acid as a precursor of platinum, and sodium citrate as a complexing agent to react in an autoclave to prepare a catalyst;

The platinum content of the precious metal electrocatalyst carried by the composite carrier described in step (2) is 10wt%, and SiO Content is 10%

(3) Preparation of humidification-free membrane electrode: same as Example 1.

(4) Membrane electrode test: Same as Example 1, but the battery temperature is 60°C.

The results obtained are shown in Table 1. Within 5 hours, the current density decreased from 870mA/cm ² to 430mA/cm ² , and within 20 hours to 310mA/cm ² , showing a certain effect of avoiding humidification.

Example 6

(1) Preparation of composite carrier: Take 0.155g of tetraethyl orthosilicate and add it to 3ml of ethanol, then add 1 gram of XC-72R carbon black that has been oxidized and heat-treated, and stir at room temperature for 15 minutes to make orthosilicic acid and carbon black uniform Disperse, then in a vacuum oven at 40°C, evacuate to remove residual ethanol, then heat-treat at 400°C for 3h under an inert atmosphere, and cool; that is, a carbon composite carrier material containing silicon dioxide is obtained; it can be expressed as SiO2 /XC-72R or SiO2/C;

(2) Preparation of electrocatalyst: with the composite carrier prepared in step (1) as the carrier, the organosol method described in the patent (ZL 200510102382.X) was used to prepare the noble metal electrocatalyst supported by the composite carrier; the specific method The method is: using a mixture of acetone and ethylene glycol as a solvent, ethylene glycol as a reducing agent, chloroplatinic acid as a precursor of platinum, and sodium citrate as a complexing agent to react in an autoclave to prepare a catalyst;

The platinum content of the noble metal electrocatalyst carried by the composite carrier described in step (2) is 60wt%, and the SiO2 content is 3wt%;

(3) Preparation of humidification-free membrane electrode: same as Example 1.

(4) Membrane electrode test: Same as Example 5.

The obtained results are shown in Table 1. Within 5 hours, the current density decreased from 920mA/cm ² to 730mA/cm ² , and within 20 hours to 705mA/cm ² ; showing a good humidification-free effect.

Example 7

In addition to using ethyl orthosilicate and n-butyl titanate instead of ethyl orthosilicate, the catalyst composition is Pt/SiTiO _x /C, wherein Si:Ti=1:1, the content of titanium silicon oxide is 3.5%, platinum Content is 25wt%, other are all identical with embodiment 1.

As shown in Table 1, within 5 hours, the current density dropped from 900mA/cm ² to 750mA/cm ² , and then remained basically unchanged for 20 hours, showing a good effect of avoiding humidification.

Example 8

Except that n-butyl zirconate is used instead of n-butyl titanate, the catalyst composition is Pt/SiZrO _x /C, wherein Si: Zr=1:1, the content of zirconium silicon oxide is 3.5%, and the others are the same as in Example 7 .

As shown in Table 1, within 5 hours, the current density decreased from 920mA/cm ² to 730mA/cm ² , and then remained basically unchanged for 20 hours, showing a good effect of avoiding humidification.

Example 9

The catalyst composition is Pt/ _SiMoOx /C, wherein Si:Mo=1:1, molybdenum-silicon oxide content is 3.5%, and the others are the same as in Example 7, except that organic molybdate is used instead of n-butyl titanate.

As shown in Table 1, within 5 hours, the current density dropped from 930mA/cm ² to 760mA/cm ² , and then remained basically unchanged for 20 hours, showing a good effect of avoiding humidification.

Example 10

Except that organic tungstate is used instead of n-butyl titanate, the catalyst composition is Pt/ _SiWOx /C, wherein Si:W=1:1, the content of molybdenum silicon oxide is 3.5%, and the others are the same as in Example 7.

As shown in Table 1, within 5 hours, the current density decreased from 920mA/cm ² to 730mA/cm ² , and then remained basically unchanged for 20 hours, showing a good effect of avoiding humidification.

Example 11

Directly dissolving cerium nitrate in ethanol without using n-butyl titanate, the catalyst composition is Pt/SiCeO _x /C, wherein Si: Ce=1:1, the content of cerium silicon oxide is 3.5%, and others are the same as in the examples 7 is the same.

As shown in Table 1, within 5 hours, the current density dropped from 890mA/cm ² to 740mA/cm ² , and then remained basically unchanged for 20 hours, showing a good effect of avoiding humidification.

Example 12

(1) Preparation of the composite carrier: the same as in Example 1 except that the amount of ethyl orthosilicate is 0.155 g.

(2) Preparation of electrocatalyst: with the composite carrier prepared in step (1) as the carrier, the electrocatalyst of composite carrier loaded with noble metal was prepared by solid phase reduction technology; the specific method is: a certain amount of chloroplatinic acid dissolved In the mixed solvent of ethanol and water, add sodium citrate complexing agent, add the composite carrier prepared in step (1), ultrasonic for 15 minutes, and then dry in a vacuum oven at 70°C; spray sodium formate solution under stirring, 40°C Dry in a vacuum oven, then raise the temperature to 100°C to reduce platinum; obtain an electrocatalyst;

In the prepared electrocatalyst, the platinum content is 25wt%, and the SiO2 content is 3wt%.

(3) Preparation of humidification-free membrane electrode: same as Example 1.

(4) Membrane electrode test: Same as Example 1.

The results obtained are shown in Table 1. Within 5 hours, the current density decreased from 880mA/cm ² to 630mA/cm ² , and within 20 hours to 603mA/cm ² , showing a certain effect of avoiding humidification. However, the overall performance is not as good as that of similar catalysts prepared by the organosol method.

Example 13

(1) Preparation of the composite carrier: the same as in Example 1 except that the amount of ethyl orthosilicate is 0.155 g.

(2) Preparation of electrocatalyst: with the composite carrier prepared in step (1) as the carrier, the electrocatalyst of the composite carrier loaded with noble metal was prepared by impregnation; the specific method is: a certain amount of chloroplatinic acid is dissolved in ethanol Mixed solvent with water, adding sodium citrate complexing agent, adding the composite carrier prepared in step (1), ultrasonication for 15 minutes, and then drying in a vacuum oven at 70°C; the dried sample was placed in a tube electric furnace , and reduced at 200°C for 3 hours to obtain an electrocatalyst;

In the prepared electrocatalyst, the platinum content is 25wt%, and the SiO2 content is 3wt%.

(3) Preparation of humidification-free membrane electrode: same as Example 1.

(4) Membrane electrode test: Same as Example 1.

The results obtained are shown in Table 1. Within 5 hours, the current density decreased from 910mA/cm ² to 670mA/cm ² , and within 20 hours to 620mA/cm ² , showing a certain effect of avoiding humidification. However, the overall performance is not as good as that of similar catalysts prepared by the organosol method.

The test result contrast of each embodiment of table 1

Example catalyst Initial current density mA/cm ² Current density mA/cm ² after 5 hours Current density mA/cm ² after 20 hours 1 Pt/SiO ₂ /C (0.3%SiO ₂ ) 910 550 480 Compared Pt/C (JM40%) 900 88 - 2 Pt/SiO ₂ /C (3%SiO ₂ ) 910 740 710 3 Pt/SiO ₂ /C (6%SiO ₂ ) 910 670 610(10 hours) 4 Pt/SiO ₂ /C (9%SiO ₂ ) 920 730 710 5 Pt/SiO ₂ /C 870 430 310 6 Pt/SiO ₂ /C 910 730 705 7 Pt/SiTiO _x /C 900 750 725 8 Pt/SiZrO _x /C 920 730 710 9 Pt/SiMoO _x /C 930 760 730 10 Pt/SiWO _x /C 920 730 700 11 Pt/SiCeO _x /C 890 740 710 12 Pt/SiO ₂ /C (solid phase reduction) 880 630 603 13 Pt/SiO ₂ /C (impregnation method) 910 670 630

Claims (9)

1. An electrocatalyst for fuel cell membrane electrodes, characterized in that: the electrocatalyst is prepared by carrying noble metals on a composite carrier, and the composite carrier is a carbon carrier deposited by a water-retaining substance; in the electrocatalyst, The content of the water-retaining substance is 0.3-10wt%; the content of the precious metal is 10-60wt%. 2. The electrocatalyst according to claim 1, characterized in that: the water-retaining substance is one or more of silica, titanium dioxide, ceria, zirconium dioxide, tungsten trioxide and molybdenum trioxide . 3. The electrocatalyst according to claim 1 or 2, characterized in that the noble metal is platinum. 4. A method for preparing an electrocatalyst for a fuel cell membrane electrode, characterized in that it comprises the following steps: (1) Dissolve the organic precursor of the water-retaining substance in a volatile organic solvent, then add the pretreated carbon carrier, stir at room temperature to mix the organic precursor of the water-retaining substance evenly on the carbon carrier, and then place it In a vacuum drying oven at 40-70°C, remove the volatile organic solvent by vacuuming, take it out and heat-treat it at 200-600°C for 1-5h under an inert gas atmosphere, and obtain a carbon carrier deposited by a water-retaining substance after cooling, that is, a composite carrier; (2) using the composite carrier prepared in step (1) as a carrier to prepare an electrocatalyst for the composite carrier to carry precious metals; In the electrocatalyst, the content of the water-retaining substance is 0.3-10wt%, and the content of the noble metal is 10-60wt%. 5. The preparation method according to claim 4, characterized in that the step (2) adopts organosol method, impregnation method or solid phase reduction method to prepare the electrocatalyst loaded with noble metal on composite carrier. 6. The preparation method according to claim 4 or 5, characterized in that the water-retaining substance is one or one of silica, titanium dioxide, ceria, zirconium dioxide, tungsten trioxide and molybdenum trioxide above. 7. The preparation method according to claim 4, characterized in that the volatile organic solvent is ethanol or acetone. 8. A fuel cell membrane electrode, comprising a proton exchange membrane, an anode and a cathode, the proton exchange membrane being sandwiched between the two electrodes, characterized in that the electrocatalyst according to claim 1 is used as the anode catalyst. 9. The fuel cell membrane electrode according to claim 8, characterized in that the electrocatalyst according to claim 1 is used as the cathode catalyst.

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